Stabilization of aqueous dispersions of polymers of vinyl esters



Patented- Jan. 11, 1944 I STABILIZATION F AQUEOUS DISPERSION 8 OFPOLYMERS F VINYL ESTERS Harry. T. Neher, Bristol, and William R. Conn,Philadelphia, Pa., asslgnors to Riihm & Haas Company, Philadelphia, Pa.

No Drawing.

Application July 5, 1941,

Serial No. 401,286

4 Claims. (01. 280-32) This invention relates to the stabilization ofaqueous dispersions of polymers 01' a vinyl ester and or co-polymers ofa vinyl ester and another polymerizable unsaturated material compatibletherewith and capable oi copolymerizing therewith.

Methods have already been developed for the preparation of aqueousdispersions of vinyl esters and mixed polymers prepared with vinyl.esters. Such dispersions are generally satisfactory for a short timeafter their manufacture, but they deteriorate rapidly on storage. Insome cases the particles coalesce with the formation of two layers; inother cases gels are formed and the emulsions "set up." Either type ofinstability destroys the utility of the dispersion. -These phenomena areparticularly troublesome in that the storage life" of different batchesmade in apparently identical manner varies and the life of a dispersioncannot be foretold.

It has now been found that stability of an aqueous dispersion 01' apolymerized vinyl ester or of a co-polymer containing a vinyl ester isgreatly improved if the acidity developed during polymerization isremoved by addition 01' a dilute solution 01' an alkaline compoundhaving a monovalent cation such as sodium hydroxide or a mixture ofsodium hydroxide and an alkaline buffering salt, such as sodium acetate.The optimum degree of stabilization results by first adding a dilutealkaline solution until the dispersion is slightly alkaline and heatingthe alkaline dispersion to induce hydrolysis of a small part of thepolymeric vinyl ester. Generally, hydrolysis of 2% to 5% 01 the vinylpolymer is suflicient to ensure excellent stability over a long periodof time.

A process is described in U. S. Patent No. 2,127,- 135, issued August16, 1938, by means of which an exact and easy control of polymerizationof vinvyl esters is made possible. A vinyl ester or mixtur of monomericester and another polymerizable substance is emulsified in an aqueoussolution containing an emulsifying agent. A

- under pressure, partial saponification or hydrolysis occurs and thedispersion then possesses a remarkable degree 01' stability. It remainsneutral or slightly alkaline for a long period of time.

In adjusting alkalinity and in hydrolyzing a portion or the dispersedpolymer there may be used any soluble alkaline material such as sodiumhydroxide, potassium hydroxide, ammonium hydroxide, quaternary ammoniumhydroxide such as benzyl trimethyl ammonium hydroxide, sodium carbonate,or other strongly alkaline compound having a monovalent cation or sucha1- kalies in conjunction with a buffer salt such as ammonium acetate,sodium acetate, or the like. It is generally undesirable to use analkaline material which causes precipitation with a product oi.hydrolysis. The alkaline material should be added to the aqueousdispersion in the form of a dilute solution. The effect of concentratedsolutions is frequently to cause an immediate coagulation. It ispreferred to add the alkaline agent in such amount and concentrationthat the range oi pH oi! the dispersion is between 7 and 12. A high pHis overcome by hydrolysis of the polymer and it is not necessary tohydrolyze an excessive amount or polymer to obtain a stability.

Further details of stabilizing action are shown in the followingillustrative examples:

Example 1 In a live-liter flask equipped with agitator and refluxcondenser there was placed a solution of 25 grams of the sodium salt ofdiisobutyl phenoxyethoxyethoxy ethyl sulfonate in 360 ml. of distilledwater. There were then separately prepared the following:

(a) An emulsion or 1050 g. of vinyl acetate in a solution of 101 g. ofdiisobutyl phenoxyethoxyethoxyethyl sodium sultonate in 1440 ml. ofdistilled water; and

(b) A solution of 5.3 g. of ammonium persulfate in 150 ml. of distilledwater.

To the solution in the five-liter flask there was then added 212 g. ofthe vinyl acetate emulsion and 13 g. of the ammonium persulfatesolution. The mixture was stirred and heated in the flask until atemperature of 74 C. was reached at which temperature a violent reactiontook place. When this reaction had subsided, the rest of the vinylacetate emulsion and of the persulfate solution was added to thereaction flask during a period of about one hour. The temperature roseto about C1 as a result of the heat generated by thepolymerization-reaction. After the addition was completed, heat wassupplied by a boillng water bath to raise the temperature to 96 C. Thepressure in the flask wasthen reduced and 40 ml. of liquid removed bydistillation. The dispersion was cooled to 55 C. and filtered. A sampleoi this dispersion was set aside and observed for stability. It had a pHof 2.5; titration cated that not more than 1.2% of the polyvinyl I esterhad been hydrolyzed during that time.

A third sample was treated with one=third of its weight of 0.53 N ofsodium hydroxide solution and heated for one hour at 65 C. and then at75 C. for nve minutes. This sample remained stable during a test periodof over 305 days and had a pH of 6.5 at the end of this period.

A fourth sample was neutralized with sodium hydroxide as in the case ofthe second sample and 2.5% of polyvinyl alcohol added to the neutralsolution. This sample had a stability identical with that of the secondsample, indicating that added polyvinyl alcohol had no value instabilizing the emulsion.

Example 2 An emulsion was prepared from 675 g. 01' vinyl acetate and 450g. of ethyl methacrylate in a solution of 108 g. of isooctylphenoxyethoxyethoxyethyi sodium sulionate in 1483 ml. 01' distilledwater. There was also prepared a solution of 11.3 g. of ammoniumpersuliate in 100 ml. of water. There was then prepared in a five-literflask equipped with agitator and reflux condenser a solution of 2'1 g.oi iso-octyl phenoxyethoxy ethoxyethyl sodium sulionate in 370 ml. ofwater. To the latter solution there was added 400 g. oi the aboveemulsion and 15 ml. of the ammonium persulfate solution. The mixture wasstirred and heated until the initial reaction was complete. The rest ofthe emulsion and the persuliate solution were added over a period oithree hours while the resulting mixture was stirred and main tained at'75-84 C. The temperature was then raised to 95 C. by means of a boilingwater bath. The pressure in the flask was reduced and 35 ml. oi liquiddistilled therefrom. The emulsion was cooled to 75 0., half of thedispersion removed, and the balance treated with a solution of 13 g. ofsodium hydroxide in 490 ml. of water. The temperature of the dilutedalkaline dispersion was maintained at 60 C. for an hour. This par tiallyhydrolyzed sample was stored for a period of ten months withoutseparation or gelatlon occurring and without hydrolysis.

A sample of the original dispersion was 39% hydrolyzed within 10 months.

Another sample of the original dispersion was neutralized with a 0.47 Nsodium hydroxide solu tion. It began to hydrolyze within three months,but hydrolysis proceeded only very slowly.

Example 3 An emulsion was prepared from 788 g. of vinyl acetate, 263 g.of ethyl acrylate, 101 g. of diisobutyl phenoxyethoxyethoxyethyl sodiumsulionate, and 1440 ml. of water. 212 g. or this emulsion was added to asolution of g. of diisobutyi phenoxyethoxyethoxyethyl sodium sulionatein 360 m1. at water in a five-liter flask equipped with a stirrer andreflux condenser. There was then added 13 ml. of a solution preparedfrom 5.8 g. of ammonium persuliate and 150 ml. of water. The contents ofthe flask was stirred and heated until a temperature of 83 C. wasreached.

The rest of the emulsion of monomer and of the persulfate solution werethen gradually added to the flask during a period of one and one-halfhours and the temperature of the mixture kept at 72-85 C. Thetemperature was then raised to 96 C.. the pressure in the flask reducedand 40 ml. oi. liquid distilled therefrom. The resulting dispersion wascooled to 50 C. and filtered.

A sample of the dispersion as thus prepared was set aside and observedfrom time to time. It hydrolyzed slowly but progressively so that after305 days 39% of the polymer had hydrolyzed, calculated from the acidliberated.

A sample of 704 g. was stirred with 295 ml. of 0.47 N sodium hydroxidesolution at 60 C. for an hour. This preparation was entirely stable overa ten-month test period and it still had pH of 7.12at the end of thistime.

Example 4 An emulsion was prepared from 1068 parts 01' distilled water,67.5 parts of octylphenoxyethoxyethoxyethyl sodium sulfonate, 3.5 partsor ammonium persuifate, and .700 parts of vinyl acetate. A portion oi.141 parts of this emulsion was added to a solution of 16.5 parts ofoctylphenoxyethoxyethoxyethyl sodium suli'onate in 244 parts ofdistilled water, which was contained in a vessel equipped with agitatorand reflux condenser. The vessel was then heated until the temperaturereached 0., at which time polymerization was complete. The rest of theoriginal emulsion was then gradually added while the temperature wasmaintained between 80 and C. The temperature was then. raised to 96 C.and a stream or air passed through the polymerized dispersion to removetraces of unpolymerized vinyl acetate.

Portions of the finished dispersion were then taken and neutralized with0.5 N sodium hydrox- :lde solution, 0.5 N potassium hydroxide, ammonia,0.5 N sodium carbonate solution and 0.5 N triethanolamine solution.These portions were stored and remained stable over a long period oftime. On the other hand, the addition of barium hydroxide or calciumhydroxide caused coagulation of the polymer.

In place of the vinyl acetate shown in the I above examples there may beused other vinyl esters. such as vinyl propionate,butyratepchloropropionate, etc., alone, or in combination, or inconjunction with other polymerizable unsaturated substances which arecompatible and which are capable of forming co-polymers such as theacrylate or methacrylate esters, as for example the methyl, ethyl,propyl, butyl, octyl, dodecyl, cetyl, benzyl, cyclohexyl, etc. esters,acrylonitrile, methacrylonitrile, acrylic or methacrylic acid, etc.

We claim:

1. The process of stabilizing an aqueous dispersion of solid polyvinylacetate prepared by the polymerization of an aqueous emulsion ofmonomeric vinyl acetate followed by the removal of unpolymerized vinylacetate, which comprises adlusting the pH of the dispersion to a value01 from 7 to 12 by the addition of an alkaline com-,

pound having a monovalent cation, and inducmg a partial hydrolysis equalto from 2 to 5% of the vinyl ester polymer by heating the alkalinedispersion.

3. The process of stabilizing an aqueous dispersion or a solid vinylester polymer prepared by the polymerization of an aqueous emulsion 01vinyl acetate and a methacrylic acid ester of a saturated alcoholfollowed by the removal of unpolymerized monomeric material. which comprises adjusting the pH 0! the dispersion to a value of from 7 to 12 bythe addition of an alkaline compound having a monovalent cation. andinducing apartialhydrolysls equaltoirom'ato 6%. o! the vinyl esterpolymer by heating the alkaline dispersion.

4. The process oi. stabilizing an aqueous dispersion of a solid vinylester polymer selected from the group consisting oi polymers of vinylesters of lower saturated fatty acids and copolymers thereotwith thenitrile andsaturated alco- 10 hol esters of acrylic and methacrylicacid, which dispersion is prepared by the polymerization oi anaqueousemulsion of the monomeric'materials followed by the removal orunpolymerized monomeric material, which comprises adjusting the 15 pH ofthedispersion to a value of from 7 to 12 by the addition of an alkalinecompound having.

a monovalent cation, and inducing a partial hydroiysis equal to from 2to 5% 01' the vinyl ester polymer by heating the alkaline dispersion.

HARRY '1. NEHER. WILLIAM R. CONN.

